In flattening a sheet workpiece such as a silicon wafer, double-side polishing apparatuses and double-side lapping apparatuses have been used previously.
In the double-side polishing apparatus, for example, a discoid carrier with a planetary gear at the periphery is disposed between upper and lower turn tables each pasted with a polishing pad made of urethane foam or non-woven fabric. This carrier is made to rotate and revolve around a sun gear by mutually rotating the sun gear and an internal gear, which engage with the planetary gear, while the carrier holding a workpiece in its holding hole. The rotation and revolution of carrier and rotations of the upper and lower turn tables make the workpiece rub with the upper and lower turn tables to polish the upper and lower surfaces of the workpiece at the same time. During the polishing, polishing slurry is supplied from a plurality of holes provided in the upper turn table to perform polishing efficiently.
The upper turn table is provided with an up-and-down motion mechanism, which allows the upper turn table to move upward and downward, (e.g., Patent Document 1). While the upper turn table is at the raised position where it has been moved upward, the carrier is disposed on the lower turn table, and a workpiece is held by the carrier. The upper turn table may also be moved downward from the raised position to a position of intermediate height, where the downward movement of the upper turn table is stopped, to give appropriate gap between the upper turn table and the lower turn table, and a cleaning nozzle is inserted between the upper turn table and the lower turn table to clean the polishing surfaces of the polishing pads. In the position of intermediate height, the polishing surfaces of the polishing pads may be subjected to dressing by inserting a dresser head between the upper turn table and the lower turn table to regulate the surface condition of the polishing pads.
In such cleaning and dressing of the polishing surface of the polishing pad, the cleaning nozzles and the dresser head each frequently have an area that is apparently smaller than that of the polishing surface of the polishing pad pasted on the turn table. Such a head is attached to an arm, and this arm can move the head from the outermost periphery of the turn table to the innermost circumference by the linear motion or rotating movement thereof. This motion, together with simultaneous rotation of the upper and lower turn tables, allow these heads to clean or dress the whole polishing surface.
With high integration of semiconductor devices in recent years, silicon wafers have been more strictly required to have flatness and surface quality. To fulfill such requirements for the quality, it is important to maintain the polishing surface of a double-side polishing apparatus and a double-side lapping apparatus at an appropriate condition continually.
In actual processes, however, the operation may be followed by residual substances remained on the polishing surface in lapping, for example, which obstruct the flow of slurry; clogging of the surface of the polishing pad in double-side polishing, for example; as well as degradation and deformation of the surface resin of the polishing pad itself. These changes of the process conditions cause to induce degradation and fluctuation of wafer quality.
To prevent such degradation and fluctuation of wafer quality, it is important to maintain the polishing surface in uniform and good condition. Accordingly, it is usual to regularly perform cleaning of the polishing surface and dressing of the polishing pad described in background art.
The apparatuses, however, have been becoming larger due to an increase of wafer diameter, which makes it more difficult to maintain the polishing surface with large area uniformly.
In many cases, the upper turn table of a double-side polishing apparatus or a double-side lapping apparatus is connected to a cylinder shaft provided at the upper part of the apparatus through a universal joint or a spherical bearing so as to change the angle optionally. This intends to perform polishing of a workpiece, in which uniform loading can be applied continually from the upper turn table when, the workpiece or the carrier holding the workpiece has in thickness variation.